4. Choosing the Control Group: Placebo, Usual Care, and Equipoise
After this lesson you can
- Specify an intervention by content, dose, delivery, duration and adherence rule
- Match each of six control options to the question it answers
- Separate expectation and attention from natural course, regression and measurement in a control arm
- Apply equipoise and the three ethical principles to the choice of control
- Define and document usual care, adherence and contamination
Video coming soon
Lessons publish daily from November 17, 2026.
This lesson shows how to specify an intervention precisely enough for another unit to deliver it and compares six control options and the question each answers. It explains what a placebo arm contains, defines clinical equipoise with the three ethical principles, and defends a documented usual-care control in an add-on design.
Questions and answers
Questions a learner would ask about this lesson. Think through your own answer before you open each one.
- What does it mean to specify an intervention?
Show answer
An intervention is specified by content, dose, delivery, duration and an adherence rule, not by a name. The test is whether another unit could deliver it from the protocol. In the fictional Oakhaven trial the program is twelve monthly sessions over twelve months, delivered in person by trained clinic staff from a session manual, with adherent defined as at least nine of twelve sessions.
- What are the six control options?
Show answer
No treatment, placebo, active control, usual care, add-on and dose comparison. Each answers a different question: better than nothing, better than its own appearance, better than or as good as the standard, better than current practice, or how much is enough. A positive trial proves only that the intervention beat its particular control.
- Isn't improvement in a placebo arm just the placebo effect?
Show answer
No. A control arm contains five things at once: expectation of benefit, attention from being in a trial, the natural course of the condition, regression to the mean, and measurement and its repetition. A matching placebo, identical in look, taste and schedule, cancels expectation and attention.
- What is clinical equipoise?
Show answer
It is genuine uncertainty in the expert community about which arm is better, and it is the justification for randomizing. It is held by the community, not one investigator, so one clinician's belief in the program is not evidence. Equipoise must hold at the start, and the data monitoring committee watches it as evidence accumulates.
- Why did Oakhaven choose an add-on to usual care rather than a placebo-only arm?
Show answer
When an effective standard exists and withholding it risks serious or lasting harm, a placebo-only arm is usually unacceptable. In the add-on design both arms receive usual care in full and the program arm also receives the sessions, so nothing effective is withheld. Usual care is defined as the clinic's documented routine, not assumed, so the control is never "nothing."
Practice quiz
- Question 1The Oakhaven program is delivered as:
- Question 2Which five parts specify an intervention?
- Question 3A trial compares a new treatment with an established treatment that both arms know to be active. This is:
- Question 4What question does a dose-comparison trial answer, and what can it not show?
- Question 5A matching placebo controls for:
- Question 6How does the placebo effect differ from regression to the mean?
- Question 7Clinical equipoise means:
- Question 8When an effective standard treatment exists, the usual comparison is:
- Question 9An adherent Oakhaven participant attends at least:
- Question 10Some usual-care participants obtain a version of the program at another clinic. What is this called, and how does the lesson handle it?
Saved in your browser only: no account, no server.
Design of Clinical Studies is education only. Every lesson follows the fictional Oakhaven Adherence Trial with invented numbers; the course uses no real data and cites no real studies.